1. Technical Field
This invention relates to graft copolymers and processes for their preparation. In another aspect, this invention relates to immobilization of proteins on synthetic polymers and also to methods of immunoassay based on such immobilization. This invention also relates to polymers with proteins immobilized on the surface thereof.
2. Description of the Related Art
Processing and/or production of polymers using wiped-surface reactors such as screw extruders and twin-screw extruders is well known (such processing is often referred to as reactive extrusion). Twin-screw extruders and their use in continuous processes such as graft polymerization, alloying, bulk polymerization of vinyl monomers, and condensation and addition reactions are generally described in Plastics Compounding, January/February 1986, pp. 44-53 (Else et al.) and Plastics Compounding, September/October 1986, pp. 24-39 (Frund et al.). Graft reactions are said to be carried out by first melting a polymeric species in the initial stages of an extruder, injecting a peroxide catalyst into the extruder, and mixing in a monomer under high shear conditions. Advantages of the twin-screw extrusion process are said to include narrow distribution of molecular weight, improved melt-flow properties, consistent process control, and continuous processing.
Graft polymerization reactions of polyolefins with various monomers using wiped-surface reactors are known. Such grafting is said to be useful in providing a polymer adduct with functionality to allow further modification of structure and properties, and general mechanistic proposals regarding the formation of these "mechanochemically synthesized" adducts are discussed in connection with the grafting of maleic anhydride onto polypropylene in Polymer Prep., 1986, 27, 89 (Al-Malaika). Particular free radical graft polymerization reactions have been reported. For example, U.S. Pat. No. 3,177,270 (Jones et al.) discloses a process of preparing graft copolymers by malaxing an olefin polymer at a temperature between 110.degree. C. and 250.degree. C. while contacting the polymer with a minor proportion of a mixture comprising a monovinyl aromatic compound and optionally one or more other monomers such as acrylic acid, methacrylic acid, acrylonitrile, methyl methacrylate, methacrylonitrile, or maleic anhydride, the mixture having dissolved therein an organic peroxide. British Pat. No. 1,393,693 (Steinkamp et al.) discloses the use of a single-screw extruder to graft monomers such as maleic anhydride and acrylic acid onto polyolefins such as polypropylene in the presence of a suitable free radical initiator such as an organic peroxide. The product graft copolymers are said to have a melt flow rate (MFR) of at least 50% greater than the MFR of the base polymer.
U.S. Pat. No. 4,003,874 (Ide et al.) discloses modified polyolefins obtained by adding an unsaturated carboxylic acid or an anhydride thereof and an organic peroxide to a polyolefin and melting these components in an extruder. The polyolefin so obtained adheres to glass fibers.
U.S. Pat. No. 4,146,529 (Yamamoto et al.) discloses a process for the production of modified polyolefins by combining a polyolefin with one or more carboxylic acids or their anhydrides in the presence of a radical producing agent in an extruder and in the presence of an organosilane.
U.S. Pat. No. 4,228,255 (Fujimoto et al.) discloses a method for crosslinking a polyolefin, the polyolefin being a low density polyethylene or a polyolefin mixture containing a low density polyethylene, comprising reacting the polyolefin with an organic silane and an organic free radical initiator to form a silane-grafted polyolefin, then mixing the silane-grafted polyolefin with a silanol condensation catalyst. The mixture is extruded with heating in a single-screw extruder to obtain a crosslinked polyethylene.
Among the myriad properties of some synthetic polymers is their ability to reversibly bind proteins. Many techniques for assay of protein-containing substrates are based on such binding. Enzyme linked immunosorbent assay, described in "Biomedical Applications of Immobilized Enzymes", Vol 2 T. M. S. Chang, Ed. Plenum Publishing Corp., (Engvall) is but one such technique. ELISA and other enzyme immunoassay techniques such as those described in Clin. Chem. 1976, 22, 1243 (Wisdom) generally use a material such as glass, polycarbonate, or polystyrene as a solid-phase immune adsorbent, which immobilizes one member of an immunological pair. The subsequent assay relies on competitive binding of the other member of the immunological pair in labeled and unlabeled form, to the immobilized member. One recognized disadvantage of the use of such techniques is that the immobilized protein is only physically adsorbed to the immune adsorbent such that adsorbed protein can be washed off to various degrees by rinsing or contact with aqueous buffer solutions. A decrease in assay accuracy, precision, and sensitivity can result from such "leakage" of the adsorbed protein.